BATC - Forum

A place for ATV enthusiasts to get together and discuss all things Television. NOTE - all postings remain the copyright of the author, please get their permission before copying and publishing elsewhere.

Why can't the Portsdown be made to TX on 50 MHz? The LO goes down to 35MHz. Is it the modulator chip?

My receiver PCB (Noel has one now and is patiently waiting for me to send him the schematic) requires a 400MHz LO.

Converter prototype.jpg (318.87 KiB) Viewed 1187 times

Plan is to use the spare output from the Portsdown in CW mode. It filters 50-70MHz, amplifies and converts it to 450 - 470MHz for input to the Minitiouner. There are many different ways you could use the board - no requirement to stick with it's intended use. For a TX converter for example. It can't make tea.

The problem with the Portsdown is that the QPSK modulator chip is only in-spec from 140 - 1000 MHz. It’s just about OK at 71 MHz, but gets worse quickly below that. The constellation becomes trapezoidal.

The problem with the Portsdown is that the QPSK modulator chip is only in-spec from 140 - 1000 MHz. It’s just about OK at 71 MHz, but gets worse quickly below that. The constellation becomes trapezoidal.

Dave

I see - so we either need a RX/TX frequency converter or another modulator. My current board will do that but only if the active device is bypassed to make it bi-directional. Then there would be a need for additional gain to overcome the ~10dB losses mostly important for the RX side. Maybe easier to use two boards one passive for TX, one active for RX. Or I could re-design I suppose but based on the level of interest so far I doubt there is any demand. The Pluto and Lime can do 50MHz and both are about to re breadily available again.